The present invention relates to a plant culture apparatus for artificially culturing a plurality of plants such as vegetables or the like.
Conventionally plants such as vegetables are primarily cultured constant amount of harvest because the amount of harvest increases or decreases according to the relationship between the insolation or solar radiation and rainfall or precipitation. In view of this in recent years, in the case where farm crops such as vegetables or the like are cultured, the method of hydroponic culture has been utilized in which a nutrient solution is used to culture the plants instead of growing the plants in soil.
The hydroponic culture is also adapted for the purposes of conserving soil fertility in the fields, enabling sequential cropping, avoiding damage by disease and noxious insects, increasing efficiency of energy use and automatization of the culture, and increase in production. The hydroponic culture is high in production cost compared to raising plants outdoors. In view of the fact that regulation or control of nutrients and treatment of a remained root are easy, however, hydroponic culture is utilized as a method of culturing vegetables such as leaf vegetables or the like.
As an example, a plant culture apparatus has been proposed as shown in FIG. 10.
The plant culture apparatus 1 comprises a body 3 within which a plurality of plants 2 being cultured are accommodated. A plurality of fluorescent lamps 4 are arranged within the body 3 and serve as an illuminating device for supplying light to the plants 2. A culture bed 5 is arranged below the fluorescent lamps 4, and the plants 2 rest on the culture bed 5.
The body 3 is formed by a box-like container made of a heat insulating material. The body 3 has its upper surface which is provided with a fluorescent-lamp accommodating section 3a. A duct 3b is arranged on an upper surface of the fluorescent-lamp accommodating section 3a, and opens to the ambient atmosphere.
The fluorescent lamps 4 are arranged at an upper portion of the body 3 and are spaced from each other at constant intervals. As shown in FIG. 11, a plurality of reflecting plates 6 are arranged respectively above the fluorescent lamps 4.
Referring back to FIG. 10, the culture bed 5 is made of a water sheet material absorbent. Furthermore, a plurality of liquid nutrient supply units 7 for the plants 2 are mounted to the culture bed 5.
When the plant culture apparatus is being used, seeds of the plants 2 to be cultured rest on the culture bed 5. The liquid nutrients are replenished to the culture bed 5 from the liquid nutrients supply units 7, and the plants 2 are cultured while the amount of light and the temperature are suitably adjusted by the fluorescent lamps 4.
As shown in FIGS. 12 and 13, voltage is applied to a pair of electrodes 4a and 4b of each of the fluorescent lamps 4. When the voltage exceeds a predetermined value, thermoelectrons 4e flow from a coil filament 4c of the fluorescent lamp 4 toward a coil filament 4d thereof. The thermoelectrons 4e occurring due to electric discharge move as indicated by the arrows in FIGS. 12 and 13, and are transduced into visible radiation when the thermoelectrons 4e pass through a phosphor or fluophor 4f which is coated on an inner surface of the fluorescent lamp 4.
With regard to heat generated due to the fluorescent lamps 4, useless or unnecessary heat is removed from the plant culture apparatus 1 and is sent to the outside through the duct 3b.
It is possible for the plant culture apparatus 1 described above to provide constant culturing conditions without variation due to natural phenomena such as the weather and the like. However, the following problems remain to be solved.
(1) In the conventional fluorescent lamps 4 which serve as the illuminating device, visible radiation is emitted from the entire length of the fluorescent lamps 4. Accordingly, the illuminating light from the respective fluorescent lamps 4 is such that the intensity of light on the culture surface is non-uniform in horizontal distribution.
That is, as shown in FIGS. 11 and 14, the intensity of light due to the light emitted from the fluorescent lamps 4 is high at a central region of the culture bed 5, and gradually falls off toward both ends of the culture bed 5. Thus, the plants 2 located at the central region of the culture bed 5 grow fastest, while the plants 2 located at both ends of the culture bed 5 grow more slowly. Accordingly, even if the seeds of the plants 2 are planted simultaneously it is impossible to culture the plants 2 uniformly due to the differences in growth rate.
(2) In spite of the fact that the reflecting plates 6 are arranged respectively above the fluorescent lamps 4, as indicated by the arrows in FIG. 11, some of the light emitted from the respective fluorescent lamps 4 is not directed toward the culture surface but instead escapes above or lateral to the fluorescent lamps 4. Thus, this energy is wasted.
(3) As shown in FIG. 15, generally, the conversion efficiency of the fluorescent lamps 4 is as follows. That is 75% (indicated by A in FIG. 15) of input power is lost as heat and this heat results in a cooling load. In the conventional heat-removing method described previously, the air within the culture space is used to remove the heat generated by the illumination. Accordingly, there is a case where the cooling load is not reduced. Thus, the conventional heat-removing method is not efficient.
(4) Heat emitted from the fluorescent lamps 4 may exert deleterious effect on the plants 2, and increases the cooling load.